The present invention relates to a semiconductor device of a resin sealing type in which a semiconductor element is sealed with a synthetic resin.
Generally, semiconductor devices of a resin sealing type are classified into a package type known as BGA (Ball Grid Array) in which a semiconductor element is mounted on a substrate composed of glass epoxy, etc., which is sealed with a resin, and a package type in which the semiconductor element is mounted on a lead frame, which is sealed with the resin.
FIG. 11 is a view showing a sectional structure of the semiconductor device of the type known as the BGA.
In the semiconductor device of the BGA type illustrated therein, a semiconductor element 31 is mounted on a substrate 30 composed of glass epoxy, etc., and a predetermined pattern 32 corresponding to an inner lead is formed on the surface (an upper surface in FIG. 11) of the substrate, on which the element is mounted. Further, a plurality of electrodes 33 are formed on the semiconductor element 31, and are connected to the patterns 32 corresponding thereto via metal wires 34. Moreover, a region peripheral to the semiconductor element 31 which includes the metal wires 34, is sealed integrally with a package resin 35.
On the other hand, patterns 36 corresponding to outer leads are formed on a surface (a lower surface in FIG. 11) opposite to the element mounted surface, and are electrically connected to the above-mentioned patterns 32 via through-holes 37 penetrating the substrate 30. Furthermore, solder balls 38 are fixed to land portions of the respective patterns 36 by using a bonding material 37. These solder balls 36 serve as electrode members for a external connection when packaging the semiconductor device on an unillustrated circuit board, etc., and are arrayed in a grid-like shape on a packaging surface (the lower surface in FIG. 11) of the substrate 30.
Incidentally, in this BGA type semiconductor device, when mounting the semiconductor element 31 for a high-speed process at a high operating frequency, there is taken a measure such as separating the ground from the power supply with the substrate 30 constructed in a multi-layered structure in order to avoid a delay of propagation of the electrical signal due to noises of radiations on a signal line.
In contrast with this, the semiconductor device using the lead frame takes a sectional structure as illustrated in FIG. 12.
In the semiconductor device of the illustrated lead frame type, a semiconductor element 41 is mounted on a die pad 40 of the lead frame. A plurality of electrodes 42 are formed on the semiconductor element 41, and are connected to inner leads 3 corresponding thereto via metal wires 44. Then, a peripheral region of the semiconductor element 41 which embraces the inner leads 43 is sealed integrally with a package resin 45. Further, outer leads 46 extend integrally with the inner leads 43 from side portion of the package resin 45. This outer lead 46 is so molded as to be crooked in a predetermined shape (a gull wing in the illustrative example) corresponding to a packaging mode of the package on the circuit board, etc.
There are, however, the following problems inherent in the above two types of semiconductor devices.
Namely, in the case of the BGA type semiconductor device, the solder balls 38 are two-dimensionally disposed, which is advantageous in terms of a layout of an increased number of pins. However, the substrate 30 defined as the base for the assembly parts is composed of glass epoxy that is comparatively expensive, and hence, as compared with the lead frame type semiconductor device with a simple structure, has a problem of increasing the costs. Further, the substrate 30 absorbs a moisture content in the air during its preservation, and therefore, if poor of an adhesion of the package resin 35 to the substrate 30, there might be problems caused by a low moisture resisting property and a slow solder heat resisting property as well, wherein an interface therebetween is exfoliated due to soldering during the substrate packaging process, and cracks tend to occur in the package resin 35 due to a mismatch in thermal expansion coefficient with respect to the substrate 30.
On the other hand, the lead frame type semiconductor device takes such a structure that the outer leads 46 largely protrude outwardly of the package resin 45, and is therefore disadvantageous in terms of downsizing the device as a whole. Moreover, the outer lead 46 is very easy to bend because of being elongate, and this type of semiconductor device is limited in terms of the layout of the increased number of pins in consideration of copulation (flatness) of a lead connecting portion when in the substrate packaging process.
Further, the lead frame serving as the base for the assembly parts is composed of the metal material, and, besides, takes the structure assuming as simple a configuration as a plate. Therefore, although lower in price than in the BGA type semiconductor device described above, the latter semiconductor device tends to cause the noises between the signals because of the lead frame taking the single-layered structure and is not suited to mount the semiconductor element 41 requiring the high-speed process. Accordingly, in that case, there is no alternative but to adopt the structure of the above-mentioned BGA type, and, as a result, there is a disadvantage of increasing the costs.